If you're a fan of a simple oil and vinegar dressing for your salad, your days of having to shake the bottle for a few seconds to mix both ingredients could soon be over. Researchers at MIT have found a way to combine water and oil-based substances so that they stay mixed for months on end.
There are several reasons why oil and water (and water-based solutions such as vinegar) resist mixing: Oil is less dense than water, creating a propensity for it to float on top of H2O; water molecules naturally knit tightly to each other using strong hydrogen bonds; and the fact that oil tends to be hydrophobic, repelling water instead of attracting it. As a result, if you want the two to mix for more than just a few minutes, you'll need to create an emulsion by vigorously shaking or vibrating the mixture to create tiny droplets that take much longer to coalesce into larger drops and eventually completely separate.
Creating an emulsion is an energy-intensive process, and expensive on an industrial scale. But the new approach developed at MIT is much cheaper and easier to implement. Instead of shaking or blasting a mixture with sound waves, they use the same science that makes your bathroom mirror fog up while you're taking a hot shower: Condensation.
Oil is first mixed with a surfactant, which is a soap-like substance that will easily bind to both oil and water molecules. The oil is placed in a chamber full of humid air and then cooled, which causes the water droplets in the air to condense and form uniform, microscopic droplets that evenly spread through the oil. By tweaking the oil and surfactant mixture just right, the water droplets can be reduced to nanoscale sizes that aren't as easily affected by gravity, producing emulsions that remain stable for months - not minutes.
Aside from revolutionising the salad industry, the research could help extend the expiration date of expensive pharmaceuticals that often contain unstable emulsion mixtures resulting in a unreasonably short shelf life.